Servicing of network software components of nodes of a cluster storage system

ABSTRACT

Described herein are method and apparatus for servicing software components of nodes of a cluster storage system. During data-access sessions with clients, client IDs and file handles for accessing files are produced and stored to clients and stored (as session data) to each node. A serviced node is taken offline, whereby network connections to clients are disconnected. Each disconnected client is configured to retain its client ID and file handles and attempt reconnections. Session data of the serviced node is made available to a partner node (by transferring session data to the partner node). After clients have reconnected to the partner node, the clients may use the retained client IDs and file handles to continue a data-access session with the partner node since the partner node has access to the session data of the serviced node and thus will recognize and accept the retained client ID and file handles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S.application Ser. No. 15/441,292, filed Feb. 24, 2017 and titled“Servicing of Network Software Components of Nodes of a Cluster StorageSystem,” which claims priority to and is a continuation of U.S.application Ser. No. 15/137,906, filed Apr. 25, 2016 and titled“Servicing of Network Software Components of Nodes of a Cluster StorageSystem,” which claims priority to and is a continuation of U.S. Pat. No.9,325,790, filed Feb. 17, 2009 and titled “Servicing of Network SoftwareComponents of Nodes of a Cluster Storage System,” which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to storage systems, and particularly, toservicing of network software components of nodes of a cluster storagesystem.

BACKGROUND OF THE INVENTION

A storage system typically comprises one or more storage devices intowhich information may be entered, and from which information may beobtained, as desired. The storage system includes a storage operatingsystem that functionally organizes the system by, inter alia, invokingstorage operations in support of a storage service implemented by thesystem. The storage system may be implemented in accordance with avariety of storage architectures including, but not limited to, anetwork-attached storage environment, a storage area network and a diskassembly directly attached to a client or host computer. The storagedevices are typically disk drives organized as a disk array, wherein theterm “disk” commonly describes a self-contained rotating magnetic mediastorage device. The term disk in this context is synonymous with harddisk drive (HDD) or direct access storage device (DASD).

The storage operating system of the storage system may implement ahigh-level module, such as a file system, to logically organize theinformation stored on volumes as a hierarchical structure of datacontainers, such as files and logical units (LUs). For example, each“on-disk” file may be implemented as set of data structures, i.e., diskblocks, configured to store information, such as the actual data for thefile. These data blocks are organized within a volume block number (vbn)space that is maintained by the file system. The file system may alsoassign each data block in the file a corresponding “file offset” or fileblock number (fbn). The file system typically assigns sequences of fbnson a per-file basis, whereas vbns are assigned over a larger volumeaddress space. The file system organizes the data blocks within the vbnspace as a “logical volume”; each logical volume may be, although is notnecessarily, associated with its own file system.

A known type of file system is a write-anywhere file system that doesnot overwrite data on disks. If a data block is retrieved (read) fromdisk into a memory of the storage system and “dirtied” (i.e., updated ormodified) with new data, the data block is thereafter stored (written)to a new location on disk to optimize write performance. Awrite-anywhere file system may initially assume an optimal layout suchthat the data is substantially contiguously arranged on disks. Theoptimal disk layout results in efficient access operations, particularlyfor sequential read operations, directed to the disks. An example of awrite-anywhere file system that is configured to operate on a storagesystem is the Write Anywhere File Layout (WAFL®) file system availablefrom NetApp, Inc. Sunnyvale, Calif. The disk arrays can include, forexample, all traditional hard drives, flash drives, or a combination ofhard drives and flash drives.

The storage system may be further configured to operate according to aclient/server model of information delivery to thereby allow manyclients to access data containers stored on the system. In this model,the client may comprise an application, such as a database application,executing on a computer that “connects” to the storage system over acomputer network, such as a point-to-point link, shared local areanetwork (LAN), wide area network (WAN), or virtual private network (VPN)implemented over a public network such as the Internet. Each client mayrequest the services of the storage system by issuing access requests(read/write requests) as file-based and block-based protocol messages(in the form of packets) to the system over the network.

A plurality of storage systems may be interconnected to provide astorage system architecture configured to service many clients. In someembodiments, the storage system architecture provides one or moreaggregates and one or more volumes distributed across a plurality ofnodes interconnected as a cluster. The aggregates may be configured tocontain one or more volumes. The volumes may be configured to storecontent of data containers, such as files and logical units, served bythe cluster in response to multi-protocol data access requests issued byclients. Each node of the cluster includes (i) a storage server (alsoreferred to as a “disk element”) adapted to service a particularaggregate or volume and (ii) a multi-protocol engine (also referred toas a “network element”) adapted to redirect the data access requests toany storage server of the cluster.

In the illustrative embodiment, the storage server of each node isembodied as a disk element and the multi-protocol engine is embodied asa network element. The network element receives a multi-protocol dataaccess request from a client, converts that access request into acluster fabric (CF) message and redirects the message to an appropriatedisk element of the cluster. In some embodiments, the disk element andnetwork element of a node comprise software components that are serviced(e.g., upgraded, re-installed, perform maintenance, repaired, etc.) fromtime to time.

Typically, clients will connect with a node for data-access sessionswith the node. During a data-access session with a node, a client mayobtain a client identifier (ID) for connecting with the network elementand one or more file handles to access files through the disk element.The client ID needs to be produced through a connection authenticationprocedure and each file handle needs to be produced through an accessrequest validation procedure. The client then uses the client ID andfile handles in subsequent access requests sent to the node. The nodealso stores session data comprising the client ID and file handles ofeach connected client, so it may recognize the client IDs and filehandles sent in the access requests. If the node does not recognize theclient ID and file handle in an access request, the node may denyprocessing of the access request.

Typically, servicing of the disk element and network element of a noderequires the serviced node to be taken offline, thereby disconnectingany client data-access sessions with the serviced node. Conventionally,upon disconnect with the serviced node, the client will drop/delete theclient ID and all file handles and the serviced node will close all openfiles accessed by the file handles. Upon reconnection with a failoverpartner node of the serviced node, the client ID needs to be reproducedthrough the connection authentication procedure and each file handleneeds to be reproduced through an access request validation procedure.Thus, servicing of the disk element and network element of each nodetypically causes substantial disruption to client data-access sessions.As such, there is a need for a less disruptive way of servicing softwarecomponents of nodes of a cluster.

SUMMARY OF THE INVENTION

In some embodiments, a servicing module residing on each node of thecluster provides less disruptive servicing of the software components ofthe nodes of a cluster. In these embodiments, each client is configuredto retain its client ID and any file handles upon disconnection with aserviced node. Each client is also configured to automatically attemptto reconnect with a partner node and attempt to re-establish thedata-access session with the partner node using the retained client IDand file handles. While the clients attempt to reconnect with thepartner node, session data (comprising the client IDs and file handles)stored in the serviced node made available to the partner node (e.g., istransferred to the partner node). After the clients have reconnected tothe partner node, the clients may use the retained client ID and filehandles to continue the data-access session with the partner node. Thisis possible since the partner node now has access to the session data ofthe serviced node and thus will recognize and accept the retained clientID and file handles. The partner node may “recognize” the receivedclient IDs and file handles by comparing and matching the receivedclient IDs to the stored client IDs and file handles in the session dataof the serviced node.

In the embodiments described herein, there is less disruption to clientsaccessing the cluster for data-access sessions during servicing ofsoftware components of the nodes of a cluster. In particular, when aserviced node is taken offline and clients are disconnected from theserviced node, the disconnected clients can continue the data-accesssessions with the partner node using the previously obtained client IDsand file handles. As such, the client ID does not need to be reproducedthrough the connection authentication procedure and each file handledoes not need to be reproduced through an access request validationprocedure.

In some embodiments, the disk element and network element of a nodecomprise software components that are serviced (e.g., upgraded,re-installed, perform maintenance, repaired, etc.). In some embodiments,the network element of a node comprises a network software componentconfigured for interacting/interfacing with clients through a networkconnection (e.g., for receiving access requests from the clients androuting the access requests to the appropriate disk element). In someembodiments, the disk element of a node comprises a storage devicesoftware component configured for interacting/interfacing with a set ofstorage devices comprising a shared storage of the cluster (e.g., forreceiving access requests from the network element and performing theaccess requests on the shared storage).

The shared storage of the cluster may be accessible by each node of thecluster. However, particular storage sub-portions of the shared storagemay be accessible only to an assigned/associated node in normaloperating conditions. For example, a system aggregate and a dataaggregate in the shared storage is typically assigned/associated foreach node for the node to access exclusively. In a failover event (suchas a particular node being offline), the data aggregate assigned to theparticular node may be made accessible to the partner node as well. Thesystem aggregate, however, is typically accessible only to theparticular node and not to the partner mode, even during a failoverevent.

In some embodiments, only the network element software component of oneor more nodes of a cluster is serviced. Servicing of the networkelements of the cluster begins with a current node (serviced node A)having a partner node (partner node B), and is repeated for each node ofthe cluster. Prior to servicing, the serviced network element of node Ahas stored session data A (e.g., comprising “original” client IDs andfile handles) to a system aggregate A in a shared storage of the clusterand the partner network element of node B has stored session data B to asystem aggregate B in the shared storage. The system aggregate A istypically accessible only to the serviced network element and the systemaggregate B is typically accessible only to the partner network element.

After servicing is initiated, the servicing module may take the servicednetwork element of node A offline, whereby all network ports of theserviced network element are closed (which forces a networkdisconnection with clients currently connected to the serviced networkelement). A network port may be implemented as a virtual interface(VIF). The VIFs of the closed network ports of the serviced networkelement may be transferred/migrated to open network ports of the partnernetwork element upon disconnection of the client connections to theserviced network element. Upon a network disconnection, each client isconfigured to begin to attempt reconnections with the partner networkelement while also retaining any client ID and file handles receivedfrom the serviced network element prior to the network disconnection.The servicing module may then begin servicing (e.g., upgrading,re-installing, repairing, etc.) of the serviced network element softwarecomponent.

The servicing module may then provide access to session data A to thepartner network element. For example, the servicing module may transfersession data A (stored in system aggregate A) to system aggregate B forstorage. Since the partner network element now has access to sessiondata A, it will recognize the client IDs sent by the clients attemptingreconnection and begin accepting the connection attempts based on thereceived client IDs and session data A. The partner network element mayrecognize the received client IDs by matching the received client IDs tothe stored client IDs in session data A. As such, re-authentication ofthe client connection and generation of new client IDs may be avoided.

The partner network element then begins receiving access requests(containing the original client ID and original file handles) from thereconnected clients and processing the access requests based on theoriginal file handles (e.g., by routing, using the original filehandles, the access requests to the appropriate disk element). As such,the partner node can access the previously accessed files using theoriginal file handles without producing new file handles for thepreviously accessed files.

This process may be repeated for each node in the cluster, whereby eachnode in the cluster is serviced one after the other. By performingservicing on one node in the cluster at a time, the entire clustersystem does not need to be taken offline, thus reducing disruption toclient data-access.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an exemplary cluster environmentin which some embodiments operate;

FIG. 2 is a schematic block diagram of an exemplary node that may beemployed in the cluster environment of FIG. 1;

FIG. 3 is a schematic block diagram of an exemplary storage operatingsystem 300 that may be implemented by the node in FIG. 2;

FIG. 4 shows a conceptual diagram of a node comprising network elementand disk element, each of the network element and disk elementcomprising a servicing module;

FIG. 5 shows a conceptual diagram of an exemplary shared storagecomprising a plurality of aggregates;

FIG. 6 is a schematic block diagram of an embodiment of an aggregate;

FIG. 7 shows a conceptual diagram of processes performed during clientdata-access sessions;

FIG. 8 shows a conceptual diagram of exemplary session data that may becollected and stored to a system aggregate;

FIG. 9A-C show conceptual diagrams of processes performed for servicingof the network element software component of one or more nodes of acluster;

FIGS. 10A-B are flowcharts of a method for performing servicing on thenetwork element software component;

FIG. 11A-C show conceptual diagrams of processes performed for servicingof the disk element software component of one or more nodes of acluster; and

FIGS. 12A-B are flowcharts of a method for performing servicing on thedisk element software component.

DETAILED DESCRIPTION

In the following description, numerous details are set forth for purposeof explanation. However, one of ordinary skill in the art will realizethat the embodiments described herein may be practiced without the useof these specific details. In other instances, well-known structures anddevices are shown in block diagram form in order not to obscure thedescription with unnecessary detail.

The description that follows is divided into seven sections. Section Idescribes a cluster environment in which some embodiments operate.Section II describes a storage operating system having a servicingmodule for servicing software components of nodes of the cluster.Section III describes a shared storage of the cluster. Section IVdescribes a client data-access session between a client and a node.Section V describes servicing of software components of nodes of thecluster. Section VI describes servicing of network software components(network elements) of nodes of the cluster. Section VII describesservicing of storage device software components (disk elements) of nodesof the cluster.

I. Cluster Environment

FIG. 1 is a schematic block diagram of an exemplary cluster 100environment in which some embodiments operate. A cluster 100 maycomprise a plurality of interconnected nodes 200 configured to providestorage services for a set of storage devices. The nodes 200 comprisevarious functional components that cooperate to provide a distributedstorage system architecture of the cluster 100. Each node 200 may beorganized as a network element 310 and a disk element 350.

The network element 310 includes functionality that enables the node 200to connect to clients 180 over a computer network 140, while each diskelement 350 connects to one or more storage devices, such as disks 130of a disk array 120. The nodes 200 are interconnected by a clusterswitching fabric 150 which, in the illustrative embodiment, may beembodied as a Gigabit Ethernet switch. An exemplary distributed filesystem architecture is generally described in U.S. Patent ApplicationPublication No. US 2002/0116593 titled METHOD AND SYSTEM FOR RESPONDINGTO FILE SYSTEM REQUESTS, by M. Kazar et al. published Aug. 22, 2002.

It should be noted that while there is shown an equal number of networkelements and disk elements in the illustrative cluster 100, there may bediffering numbers of N and/or disk elements in accordance with variousembodiments. For example, there may be a plurality of network elementsand/or disk elements interconnected in a cluster configuration 100 thatdoes not reflect a one-to-one correspondence between the N and diskelements. As such, the description of a node 200 comprising one networkelement and one disk element should be taken as illustrative only. Forexample, a node 200 may also have one network element and a plurality ofdisk elements, a plurality of network elements and one disk element, ora plurality of network elements and a plurality of disk elements.

The clients 180 may be general-purpose computers configured to interactwith the node 200 in accordance with a client/server model ofinformation delivery. That is, each client 180 may request the servicesof the node 200 (e.g., by submitting read/write requests), and the node200 may return the results of the services requested by the client 180,by exchanging packets over the network 140. The client 180 may submitaccess requests by issuing packets using file-based access protocols,such as the Common Internet File System (CIFS) protocol or Network FileSystem (NFS) protocol, over the Transmission Control Protocol/InternetProtocol (TCP/IP) when accessing information in the form of files anddirectories. Alternatively, the client may submit access requests byissuing packets using block-based access protocols, such as the SmallComputer Systems Interface (SCSI) protocol encapsulated over TCP (iSCSI)and SCSI encapsulated over Fibre Channel (FCP), when accessinginformation in the form of blocks.

In some embodiments, a client 180 connects to a node 200 for adata-access session, during which time the client 180 may receive one ormore file handles from the node 200 for accessing one or more files (asdiscussed below). Upon a network connection failure with the node 200,the client 180 may be configured to retain any received file handles fora predetermined grace time period after the initial connection failureoccurs. During this predetermined grace period, the client 180 may alsobe configured to automatically perform a predetermined number ofreconnection attempts. If a reconnection is not successful after thepredetermined number of reconnection attempts, the client 180 may beconfigured to drop/delete the previous file handle(s) obtained by theclient 180. If within the predetermined number of reconnection attempts,a reconnection is successful, the client 180 may be configured to retainthe previous file handles and re-use the file handles to access the samefiles, without needing to reproduce new file handles. This feature issometimes referred to as the “durable file handle” feature. In someembodiments, a client 180 executes a current Windows® operating systemthat implements a current network file protocol, such as Server MessageBlock (SMB) 2.0 that provides this “durable file handle” feature.

In some embodiments, the totality of storage space provided by the disks130 and disk arrays 120 of the cluster 100 comprise a total sharedstorage space (referred to as “shared storage 135”) of the cluster 100.The shared storage 135 is accessible by each disk element 350 of eachnode 200 in the cluster 100. The shared storage 135 is discussed indetail in Section III. In some embodiments, the cluster 100 may providehigh availability of service to clients 180 in accessing the sharedstorage 135. For example, the nodes 200 may be configured to communicatewith one another (e.g., via cluster switching fabric 150) to actcollectively to offset any single node 200 failure within the cluster100. In these embodiments, each node 200 may have a predeterminedfailover “partner” node 200. When a node 200 failure occurs (where thefailed node is no longer capable of processing access requests forclients 180), access requests sent to the failed node 200 may bere-directed to the partner node 200 for processing. Note that a node 200failure may occur unintentionally or intentionally (e.g., where a nodeis taken offline for servicing).

FIG. 2 is a schematic block diagram of an exemplary node 200 that may beemployed in the cluster environment of FIG. 1. A node 200 may beillustratively embodied as a storage system comprising a plurality ofprocessors 222 a,b, a memory 224, a network adapter 225, a clusteraccess adapter 226, a storage adapter 228 and local storage 230interconnected by a system bus 223. The local storage 230 comprises oneor more storage devices, such as disks, utilized by the node to locallystore configuration information, e.g., provided by one or moremanagement processes.

The cluster access adapter 226 comprises a plurality of ports adapted tocouple the node 200 to other nodes of the cluster 100. In theillustrative embodiment, Ethernet is used as the clustering protocol andinterconnect media, although it will be apparent to those skilled in theart that other types of protocols and interconnects may be utilizedwithin the cluster architecture described herein. In alternateembodiments where the network elements and disk elements are implementedon separate storage systems or computers, the cluster access adapter 226is utilized by the network element/disk element for communicating withother network elements/disk elements in the cluster 100.

Each node 200 is illustratively embodied as a dual processor storagesystem executing a storage operating system 300 that preferablyimplements a high-level module, such as a file system, to logicallyorganize the information as a hierarchical structure of named datacontainers, such as directories, files and special types of files calledvirtual disks (hereinafter generally “blocks”) on the disks. However, itwill be apparent to those of ordinary skill in the art that the node 200may alternatively comprise a single or more than two processor system.Illustratively, one processor 222 a executes the functions of thenetwork element 310 on the node, while the other processor 222 bexecutes the functions of the disk element 350.

The memory 224 illustratively comprises storage locations that areaddressable by the processors and adapters for storing software programcode and data used in some embodiments. The processor and adapters may,in turn, comprise processing elements and/or logic circuitry configuredto execute the software code and manipulate the data. The storageoperating system 300, portions of which is typically resident in memoryand executed by the processing elements, functionally organizes the node200 by, inter alia, invoking storage operations in support of thestorage services implemented by the node. It will be apparent to thoseskilled in the art that other processing and memory means, includingvarious computer readable media, may be used for storing and executingprogram instructions pertaining to the invention described herein.

The network adapter 225 comprises a plurality of ports adapted to couplethe node 200 to one or more clients 180 over point-to-point links, widearea networks, virtual private networks implemented over a publicnetwork (Internet) or a shared local area network. The network adapter225 thus may comprise the mechanical, electrical and signaling circuitryneeded to connect the node to the network. Illustratively, the computernetwork 140 may be embodied as an Ethernet network or a Fibre Channel(FC) network. Each client 180 may communicate with the node 200 over thenetwork 140 by exchanging discrete frames or packets of data accordingto pre-defined protocols, such as TCP/IP.

The storage adapter 228 cooperates with the storage operating system 300executing on the node 200 to access information requested by theclients. The information may be stored on any type of attached array ofwritable storage device media such as video tape, optical, DVD, magnetictape, bubble memory, electronic random access memory, micro-electromechanical and any other similar media adapted to store information,including data and parity information. However, as illustrativelydescribed herein, the information is preferably stored on the disks 130of array 120. The storage adapter comprises a plurality of ports havinginput/output (I/O) interface circuitry that couples to the disks over anI/O interconnect arrangement, such as a conventional high-performance,FC link topology.

Storage of information on each array 120 is preferably implemented asone or more storage “volumes” that comprise a collection of physicalstorage disks 130 cooperating to define an overall logical arrangementof volume block number (vbn) space on the volume(s). Each logical volumeis generally, although not necessarily, associated with its own filesystem. The disks within a logical volume/file system are typicallyorganized as one or more groups, wherein each group may be operated as aRedundant Array of Independent (or Inexpensive) Disks (RAID). Most RAIDimplementations, such as a RAID-4 level implementation, enhance thereliability/integrity of data storage through the redundant writing ofdata “stripes” across a given number of physical disks in the RAIDgroup, and the appropriate storing of parity information with respect tothe striped data. An illustrative example of a RAID implementation is aRAID-4 level implementation, although it should be understood that othertypes and levels of RAID implementations may be used in accordance withthe inventive principles described herein.

II. Storage Operating System

To facilitate access to the disks 130, the storage operating system 300implements a write-anywhere file system that cooperates with one or morevirtualization modules to “virtualize” the storage space provided bydisks 130. The file system logically organizes the information as ahierarchical structure of named directories and files on the disks. Each“on-disk” file may be implemented as set of disk blocks configured tostore information, such as data, whereas the directory may beimplemented as a specially formatted file in which names and links toother files and directories are stored. The virtualization module(s)allow the file system to further logically organize information as ahierarchical structure of blocks on the disks that are exported as namedlogical unit numbers (luns).

In the illustrative embodiment, the storage operating system ispreferably the Data ONTAP® software operating system available fromNetApp, Inc., Sunnyvale, Calif. that implements a Write Anywhere FileLayout (WAFL®) file system. However, it is expressly contemplated thatany appropriate storage operating system may be enhanced for use inaccordance with the inventive principles described herein. As such,where the term “WAFL” is employed, it should be taken broadly to referto any storage operating system that is otherwise adaptable to theteachings of this invention.

FIG. 3 is a schematic block diagram of an exemplary storage operatingsystem 300 that may be implemented by the node 200 in FIG. 2. Thestorage operating system 300 comprises a series of software layersorganized to form an integrated network protocol stack or, moregenerally, a multi-protocol engine 325 (network element 310) thatprovides data paths for clients 180 to access data stored on the node200 using block and file access protocols. The multi-protocol engine 325includes a media access layer 312 of network drivers (e.g., gigabitEthernet drivers) that interfaces to network protocol layers, such asthe IP layer 314 and its supporting transport mechanisms, the TCP layer316 and the User Datagram Protocol (UDP) layer 315.

A file system protocol layer provides multi-protocol file access and, tothat end, includes support for the Direct Access File System (DAFS)protocol 318, the NFS protocol 320, the CIFS protocol 322 and theHypertext Transfer Protocol (HTTP) protocol 324. A VI layer 326implements the VI architecture to provide direct access transport (DAT)capabilities, such as RDMA, as required by the DAFS protocol 318. AniSCSI driver layer 328 provides block protocol access over the TCP/IPnetwork protocol layers, while a FC driver layer 330 receives andtransmits block access requests and responses to and from the node. TheFC and iSCSI drivers provide FC-specific and iSCSI-specific accesscontrol to the blocks and, thus, manage exports of luns to either iSCSIor FCP or, alternatively, to both iSCSI and FCP when accessing theblocks on the node 200.

In addition, the storage operating system 300 includes a series ofsoftware layers organized to form a storage server 365 (disk element350) that provides data paths for accessing information stored on thedisks 130 of the node 200. To that end, the storage server 365 includesa file system module 360, a RAID system module 380 and a disk driversystem module 390. The RAID system 380 manages the storage and retrievalof information to and from the volumes/disks in accordance with I/Ooperations, while the disk driver system 390 implements a disk accessprotocol such as, e.g., the SCSI protocol.

The file system 360 implements a virtualization system of the storageoperating system 300 through the interaction with one or morevirtualization modules illustratively embodied as, e.g., a virtual disk(vdisk) module (not shown) and a SCSI target module 335. The SCSI targetmodule 335 is generally disposed between the FC and iSCSI drivers 328,330 and the file system 360 to provide a translation layer of thevirtualization system between the block (lun) space and the file systemspace, where luns are represented as blocks.

The file system 360 is illustratively a message-based system thatallocates storage space for itself in the disk array 120 and controlsthe layout of information on the array. The file system further provideslogical volume management capabilities for use in access to theinformation stored on the storage devices, such as disks. That is, inaddition to providing file system semantics, the file system 360provides functions normally associated with a volume manager. Thesefunctions include (i) aggregation of the disks, (ii) aggregation ofstorage bandwidth of the disks, and (iii) reliability guarantees, suchas mirroring and/or parity (RAID). The file system 360 illustrativelyimplements the WAFL file system (hereinafter generally the“write-anywhere file system”) having an on-disk format representationthat is block-based using, e.g., 4 kilobyte (kB) blocks and using indexnodes (“inodes”) to identify files and file attributes (such as creationtime, access permissions, size and block location). The file system usesfiles to store metadata describing the layout of its file system; thesemetadata files include, among others, an inode file. A file (datacontainer) handle, i.e., an identifier that includes an inode number, isused to retrieve an inode from disk.

All inodes of the write-anywhere file system may be organized into theinode file. A file system (fs) info block specifies the layout ofinformation in the file system and includes an inode of a datacontainer, e.g., file, that includes all other inodes of the filesystem. Each logical volume (file system) has an fsinfo block that maybe stored at a fixed or variable location within, e.g., a RAID group.The inode of the inode file may directly reference (point to) datablocks of the inode file or may reference indirect blocks of the inodefile that, in turn, reference data blocks of the inode file. Within eachdata block of the inode file are embedded inodes, each of which mayreference indirect blocks that, in turn, reference data blocks of afile.

Operationally, an access request (read/write request) from the client180 is forwarded as a packet over the computer network 140 and onto thenode 200 where it is received at the network adapter 225. A networkdriver (of layer 312 or layer 330) processes the packet and, ifappropriate, passes it on to a network protocol and file access layerfor additional processing prior to forwarding to the write-anywhere filesystem 360. Here, the file system produces operations to load (retrieve)the requested data from disk 130 if it is not resident “in core”, i.e.,in memory 224. If the information is not in memory, the file system 360indexes into the inode file using the inode number to access anappropriate entry and retrieve a logical vbn. The file system thenpasses a message structure including the logical vbn to the RAID system380; the logical vbn is mapped to a disk identifier and disk blocknumber (disk,dbn) and sent to an appropriate driver (e.g., SCSI) of thedisk driver system 390. The disk driver accesses the dbn from thespecified disk 130 and loads the requested data block(s) in memory forprocessing by the node. Upon completion of the access request, the node200 (and storage operating system 300) returns a reply to the client 180over the network 140.

It should be noted that the software “path” through the storageoperating system layers described above needed to perform data storageaccess for the client request received at the node may alternatively beimplemented in hardware. That is, in an alternate embodiment of theinvention, a storage access request data path may be implemented aslogic circuitry embodied within a field programmable gate array (FPGA)or an application specific integrated circuit (ASIC). This type ofhardware implementation increases the performance of the storage serviceprovided by node 200 in response to a request issued by client 180.Moreover, in another alternate embodiment of the invention, theprocessing elements of adapters 225, 228 may be configured to offloadsome or all of the packet processing and storage access operations,respectively, from processor 222, to thereby increase the performance ofthe storage service provided by the node. It is expressly contemplatedthat the various processes, architectures and procedures describedherein can be implemented in hardware, firmware or software.

As used herein, the term “storage operating system” generally refers tothe computer-executable code operable on a computer to perform a storagefunction that manages data access and may, in the case of a node 200,implement data access semantics of a general purpose operating system.The storage operating system 300 can also be implemented as amicrokernel, an application program operating over a general-purposeoperating system, such as UNIX® or Windows NT®, or as a general-purposeoperating system with configurable functionality, which is configuredfor storage applications as described herein.

In addition, it will be understood to those skilled in the art that theinvention described herein may apply to any type of special-purpose(e.g., file server, filer or storage serving appliance) orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings of this invention can be adapted to a variety of storagesystem architectures including, but not limited to, a network-attachedstorage environment, a storage area network and disk assemblydirectly-attached to a client or host computer. The term “storagesystem” should therefore be taken broadly to include such arrangementsin addition to any subsystems configured to perform a storage functionand associated with other equipment or systems. It should be noted thatwhile this description is written in terms of a write any where filesystem, the teachings of the present invention may be utilized with anysuitable file system, including a write in place file system.

In some embodiments, the storage server 365 is embodied as disk element350 of the storage operating system 300 to service one or more volumesof array 120. In addition, the multi-protocol engine 325 is embodied asnetwork element 310 to (i) perform protocol termination with respect toa client issuing incoming data access request packets over the network140, as well as (ii) redirect those data access requests to any storageserver 365 of the cluster 100. Moreover, the network element 310 anddisk element 350 cooperate to provide a highly-scalable, distributedstorage system architecture of the cluster 100. To that end, the networkelement and disk element include a cluster fabric (CF) interface module340 a,b adapted to implement intra-cluster communication among thenetwork element and disk element (e.g., communication between networkelement/disk element of the same node or communication between networkelement/disk element of different nodes) using CF protocol messages.

For example, the protocol layers (e.g., the NFS/CIFS layers and theiSCSI/FC layers) of the network element 310 may function as protocolservers that translate file-based and block-based access requests fromclients 180 into CF protocol messages used for communication with thedisk element 350. In some embodiments, the network element serversconvert the incoming client access requests into file system primitiveoperations (commands) that are embedded within CF protocol messages bythe CF interface module 340 for transmission to the disk elements 350 ofthe cluster 100. Notably, the CF interface modules 340 cooperate toprovide a single file system image across all disk elements 350 in thecluster 100. Thus, any network port of a network element that receives aclient request can access any data container within the single filesystem image located on any disk element 350 of the cluster.

In some embodiments, the network element 310 and disk element 350 areimplemented as separately-scheduled processes of storage operatingsystem 300. In other embodiments, the network element 310 and diskelement 350 may be implemented as separate software components/codewithin a single operating system process. Communication between anetwork element and disk element in the same node 200 is thusillustratively effected through the use of CF messages passing betweenthe network element and disk element. In the case of remotecommunication between a network element and disk element of differentnodes, such CF message passing occurs over the cluster switching fabric150.

A known message-passing mechanism provided by the storage operatingsystem to transfer information between network element/disk element(processes) is the Inter Process Communication (IPC) mechanism. Theprotocol used with the IPC mechanism is illustratively a generic fileand/or block-based “agnostic” CF protocol that comprises a collection ofmethods/functions constituting a CF application programming interface(API). Examples of such an agnostic protocol are the SpinFS and SpinNPprotocols available from NetApp, Inc. The SpinFS protocol is describedin the above-referenced U.S. Patent Application Publication No. US2002/0116593.

The CF interface module 340 implements the CF protocol for communicatingfile system commands/messages among the network element and disk elementof cluster 100. Communication is illustratively effected by the diskelement exposing the CF API to which a network element (or another diskelement) issues calls. To that end, the CF interface module 340 isorganized as a CF encoder and CF decoder. The CF encoder of, e.g., CFinterface 340 a on network element 310 encapsulates a CF message as (i)a local procedure call (LPC) when communicating a file system command toa disk element 350 residing on the same node 200 or (ii) a remoteprocedure call (RPC) when communicating the command to a disk elementresiding on a remote node of the cluster 100. In either case, the CFdecoder of CF interface 340 b on disk element 350 de-encapsulates the CFmessage and processes the file system command. As used herein, the term“CF message” may be used generally to refer to LPC and RPC communicationbetween network elements and disk elements of the cluster.

In some embodiments, the storage operating system 300 also comprises aservicing module for performing servicing on the network element 310and/or disk element 350 software components of one or more nodes 200 ofa cluster. For example, the servicing module may perform upgrading(replacing software with newer versions), re-installing, maintenance,repairing, etc. of the network element 310 and/or disk element 350software components. FIG. 4 shows a conceptual diagram of a node 200comprising network element 310 and disk element 350, each networkelement and disk element comprising a servicing module 400. Theservicing modules 400 in each network element and disk element mayoperate in conjunction to perform servicing of the network element 310and/or disk element 350 software components. For example, the servicingmodules 400 may issue CF messages or other commands to the networkelement 310 and disk element 350 to perform the methods describedherein. After initiation, the servicing modules 400 may do soautomatically (without human initiation or intervention) for one or morenodes 200 of a cluster 100 with reduced disruption to clients 180connected to the nodes 200.

The servicing module 400 may be initiated to perform the servicing ofsoftware components by administrative command. The administrativecommand may be received by a message interface module 450 comprising,for example, a user interface or command interface. The messageinterface 450 may be used to receive administrative commands (e.g., inthe form of CF messages) for managing and issuing commands to the node200. The message interface 450 then routes the received command to theproper software module(s).

As discussed above, a node 200 may have a network adapter 225 comprisinga plurality of network ports 410 (data-access ports). Each network port410 may provide a network connection between the node 200 and a client180 to provide data-access service to the client 180 over a network 140.In some embodiments, each network port 410 is implemented as a virtualcomponent comprising a virtual interface (VIF). Each network port410/VIF may have an associated unique identifier (e.g., an InternetProtocol (IP) address endpoint) within the cluster 100 that is receivedand used by the client 180 to establish the network connection. A VIFmay transparently change association from one network port 410 toanother network port 410 (within the same node 200 or across differentnodes 200) while data-access service to a client 180 continuesuninterrupted through the change. The VIF may retain the same identifier(e.g., an IP address endpoint) with the client 180 through the change ofassociation so that changes of the underlying network ports 410 occurtransparently to a client 180 connected with a VIF. As such, the networkconnection 410 with the client 180 is maintained transparently to theclient 180 as changes of association of the underlying network ports 410occur.

A VIF may provide a client interface to the network element 310 of anode. As such, in the following description and figures, a VIF issometimes conceptually described and shown as part of the networkelement 310. In some embodiments, when a network element 310 of a node200 is being serviced by the servicing module 400, any VIFs of theserviced network element 310 and serviced node 200 may changeassociation from network ports 410 of the serviced network element 310and serviced node 200 to network ports 410 of the partner networkelement 310 and partner node 200 during the servicing. In this way,data-access to any clients 180 formerly connected to the servicednetwork element 310 and serviced node 200 may continue through thepartner network element 310 and partner node 200 during the servicing.

III. Shared Storage

As discussed above, in relation to FIG. 1, the totality of storage spaceprovided by the disks 130 and disk arrays 120 of the cluster 100comprise a total shared storage space (referred to as “shared storage135”) of the cluster 100. The shared storage 135 is accessible by eachdisk element 350 of each node 200 in the cluster 100. FIG. 5 shows aconceptual diagram of an exemplary shared storage 135 comprising aplurality of aggregates, each aggregate comprising a sub-portion of thetotal available storage space of the shared storage 135.

In these embodiments, each node 200 of the cluster 100 isassigned/associated with a system aggregate 500 and a data aggregate510. For example, node A may be assigned/associated with “systemaggregate A” and “data aggregate A” and node B may beassigned/associated with “system aggregate B” and “data aggregate B.”Each system aggregate may be used for storing system information for theassociated node 200. Such system information may include session data800 comprising data collected from the network element 310 and diskelement 350 during data-access sessions with clients 180. Each dataaggregate may be used for storing client data for the associated node200, whereby clients 180 may read and write to the data.

Each node 200 may be configured to access only the system and dataaggregates assigned to the respective node 200. As such, the diskelement 350 of each node 200 may be configured to access only the systemand data aggregates assigned to the node 200. In the example of FIG. 5,the disk element 350 of node A may be configured to access and servedata from only system aggregate A or data aggregate A and the diskelement 350 of node B may be configured to access and serve data fromonly system aggregate B or data aggregate B. Therefore, in normaloperation (when node failures have not occurred), all access requests(received at any network element 310 of any node 200 in the cluster) fordata in data aggregate A are routed through the disk element 350 of nodeA (and have physical addresses/file handles that specify the diskelement 350 of node A).

In the event of a node failure, the failed node is no longer capable ofprocessing access requests (read/write requests) from clients 180 fordata in the data aggregate assigned to the failed node. In such anevent, the access requests sent to the failed node 200 may bere-directed to the predetermined partner node 200 for processing. Thepredetermined partner node 200 of the failed node may be configured toreplace the failed node by accessing and serving data in the dataaggregate assigned to the failed node (as well as the accessing andserving data in its own assigned data aggregate).

As used herein, node A is the “primary” node and the disk element 350 ofnode A is the “primary” disk element 350 that “own” and “service” datacontainers stored in data aggregate A. As used herein, node B is the“primary” node and the disk element 350 of node B is the “primary” diskelement 350 that “own” and “service” data containers stored in dataaggregate B. As used herein, node B is the partner node of node A,whereby node B and the disk element 350 of node B “own” and “service”data containers stored in data aggregates A and B upon failure of nodeA. Under normal operating conditions (where node A has not failed), nodeB and the disk element 350 of node B do not service data containersstored in data aggregate A. Note, however, that the network element 310of each node can receive access requests for data in any data aggregate510 of the shared storage 135, and will route the access requests to theappropriate disk element 350 that services the requested data.

FIG. 6 is a schematic block diagram of an embodiment of an aggregate 600(system or data aggregate) that may be used in some embodiments. Thetotal storage space of an aggregate 600 may be allocated among a set ofone or more flexible volumes 610. A flexible volume 610 may bedynamically increased or decreased in storage size within the totalstorage space of the aggregate 600. Each flexible volume 610 maycomprise one or more data containers, such as, Luns (blocks) 602,directories 604, qtrees 606, files 608, etc. The aggregate 600 isillustratively layered on top of the RAID system, which is representedby at least one RAID plex 650 (depending upon whether the storageconfiguration is mirrored), wherein each plex 650 comprises at least oneRAID group 660. Each RAID group further comprises a plurality of disks630, e.g., one or more data (D) disks and at least one (P) parity disk.

IV. Client Data-Access Session A. Client Data-Access Sessions

FIG. 7 shows a conceptual diagram of processes performed during clientdata-access sessions. During the data-access sessions, one or moreclients 180 may connect with a node 200 to access (read/write) datacontainers stored on the shared storage 135 of the cluster. As describedin some embodiments below, a file (data container) stored in the sharedstorage 135 may be accessed using a file handle. In other embodiments,however, any other type of data container stored in the shared storage135 may be accessed using a data container handle. As such, the use ofthe terms “file” and “file handle” are used for illustrative purposesonly. A network port 410/VIF of a node 200 may be used to provide anetwork connection between the network element 310 of the node 200 and aclient 180 for a data-access session.

During a client data-access session, the network element 310 and diskelement 350 of a node 200 may collect and store session data 800 to thesystem aggregate 500 associated with the node 200. FIG. 8 shows aconceptual diagram of exemplary session data 800 that may be collectedand stored to a system aggregate 500. In the example of FIG. 8, thesession data 800 is shown as a table having a plurality of entries,however, in other embodiments, the session data 800 may also be storedand organized in different forms other than a table, such as a database,file, or any other data structure.

In the example of FIG. 8, the session data 800 comprises N-Blade sessiondata 801 that is collected and stored by the N-Blade 310 and diskelement session data 802 that is collected and stored by the diskelement 350. Note that the N-Blade 310 and disk element 350 collectingand storing the session data 800 may reside on different nodes 200. Assuch, the N-Blade session data 801 and the disk element session data 802shown in FIG. 8 may be stored on different system aggregates 500. Thismay occur, for example, if a client 180 connects with the N-Blade 310 ofnode A (whereby the N-Blade stores its session data to system aggregateA) to access a file serviced by the disk element 350 of node B (wherebythe disk element stores its session data to system aggregate B). Ingeneral, the N-Blade 310 may collect and store information relating tocurrent connections with clients 180 and the disk element 350 maycollect and store information relating to files accessed by currentlyconnected clients 180.

To begin a data-access session with a node, a connection authenticationprocedure may be performed. For example, to initiate the data-accesssession with a node, the client 180 may send a connection request to thenetwork element 310. The connection request may contain, for example, auser identification/identifier (ID) and password. Upon authenticatingthe received client ID and password (e.g., by verifying that the user IDhas permission to connect to the cluster 100 and the password iscorrect), the network element 310 may produce a client ID 810 and sendthe client ID 810 to the client 180 (which stores the received clientID). Each network element 310 of each node 200 may store informationregarding each client 180 that is connected with the network element 310to its session data 801 in the associated system aggregate 500. As shownin the example of FIG. 8, the network element 310 may store the user ID805 and the client ID 810 to its session data 801 for each connectedclient 180.

In some embodiments, the client ID 810 may comprise a unique identifierproduced by the network element 310 that uniquely identifies the client180. A client 180 submitting a valid client ID, that is recognized bythe network element 310, indicates to the network element 310 that theclient 180 has already undergone the connection authenticationprocedure. In contrast, a client 180 submitting a user ID or a non-validclient ID, that is not recognized by the network element 310, indicatesto the network element 310 that the client 180 has not already undergonethe connection authentication procedure. As such, the client 180 maysubsequently use the received client ID 810 to connect and interfacewith the network element 310 (for accessing data stored in the sharedstorage 135), without having to resend the user ID and password andwithout the network element 310 having to re-authenticate the connectionand reproduce the client ID. Thus use of the client ID 810 by the client180 and recognition of the client ID 810 by the network element avoidshaving to re-perform the connection authentication procedure.

After the connection authentication procedure, the client 180 may thensend an initial access request for a particular file (referred to as“requested file N”) in the shared storage 135. The initial accessrequest may include the client ID (for interfacing with the networkelement 310), a request type (read/write), data to be written (for writerequests), and a virtual address of requested file N. The virtualaddress of requested file N may comprise a file path specifying, forexample, directory, filename, etc. Note that although the client 180 mayinterface, for example, with network element 310 of node A, the client180 may request any file in the shared storage 135 (whether the file isstored in data aggregate A or another data aggregate).

The network element 310 receives the initial access request and uses thevirtual address of requested file N to determine a disk elementidentifier (ID). The disk element ID identifies which disk element 350in the cluster is servicing the requested file N specified by thevirtual address (i.e., the primary disk element 350 in the cluster thataccesses the data aggregate 510 in which the requested file N isstored). For example, if request file N is stored in data aggregate A,the disk element ID would identify the disk element 350 of node A. Thenetwork element 310 then sends the access request, the user ID, andclient ID to the appropriate disk element 350 that services the requestfile N (as specified by the disk element ID).

The disk element 350 receives the initial access request and may performan access request validation procedure to validate the initial accessrequest (e.g., by determining permission and lock type associated withthe client submitting the initial access request). For example, the diskelement 350 may use the virtual address of requested file N to determinea file inode number for the requested file N. The disk element 350 maythen retrieve and analyze information from the file inode specified bythe file inode number. A file inode typically contains metadata for anassociated file, such as permission/security and lock metadata.

The permission metadata may specify which users or user types (e.g.,administrators) have permission to access the file. Permission metadatamay also indicate the type of access permission a user or user type has(e.g., read only, write, etc.). The lock metadata may specify what typeof lock a user or user type can obtain when accessing the file. Locktypes may include, for example, exclusive (E), shared (S), or none (N).A user/owner having an exclusive lock has exclusive read or write accessto the file (whereby all other users/processes are prevented from havingread or write access to the file). Typically, only one user is given anexclusive lock on a file. A user/owner having a shared lock has writeaccess to the file (whereby other users/processes are prevented fromhaving write access but are allowed to have read access to the file).Typically, one or more users may be given a shared lock on a file. Auser/owner having a none lock has no read or write access lock on thefile (whereby all other users/processes are allowed read or write accessto the file).

Using the received user ID and the metadata retrieved from the fileinode, the disk element 350 determines whether the received accessrequest is valid (i.e., the user/client 180 has permission to performthe specific access request on the requested file N). If so, the diskelement 350 may then perform the received access request on therequested file N (e.g., read data from or write data to file N) that isstored in its associated data aggregate 510. The disk element 350 maysend a message to the network element 310 indicating that the accessrequest has been performed.

The disk element 350 may also form a file handle for the requested fileN, the file handle comprising the disk element ID (produced by thenetwork element 310) and the file inode number (produced by the diskelement 350). The file handle of a file may comprise a physical addressindicating where the file is stored in the shared storage 135. As such,the network element 310 and disk element 350 together translate/map thereceived virtual address of requested file N (e.g., file path) to aphysical address that may be used for locating and accessing requestedfile N in the shared storage 135. The disk element 350 may send the filehandle of requested file N to the network element 310.

The network element 310 then sends the file handle of file N to theclient 180 which stores the file handle 812. Thereafter, the client 180then includes, along with the client ID, the file handle 812 (ratherthan the file path) in subsequent access requests (after the initialaccess request) for file N. Submitting the file handle (physicaladdress) of file N in subsequent access requests for file N avoids theuser/client having to re-submit the file path (virtual address) of fileN and also allows for more efficient processing of the subsequent accessrequests by the network element 310 and disk element 350. Since the filehandle provides a detailed path to where the requested file isphysically stored in the shared storage 135, the requested file may bedirectly accessed using the file handle, thereby avoiding having toagain translate/map between a file path (virtual address) and the filehandle (physical address).

The network element 310 may store the file handle 812 to its sessiondata 801 and associate the file handle 812 with the corresponding userID 805 and client ID 810 (that identify the user/client that obtainedand is using the file handle 812). The user ID 805/client ID 810 andassociated file handle 812 may comprise a single entry in the networkelement session data 801.

The disk element 350 may also store information to its session data 802in its associated system aggregate 500. As shown in the example of FIG.8, the disk element 350 may store to its session data 802 the user ID805 and the client ID 810 (received from the network element) and theassociated file handle 812. The disk element 350 may also store to itssession data 802, a permission flag 815 and lock state type 820associated with a specific combination of a particular client ID 810 (oruser ID 805) and a particular file handle 812.

Note that the user ID 805 and the client ID 810 both uniquely identify auser/client that is accessing the shared storage 135 and the file handle812 uniquely identifies a file stored in the shared storage 135. Sinceeach user/client may be simultaneously storing and using multiple filehandles (for accessing multiple files in the shared storage 135) andeach file handle may be simultaneously stored and used by multipleusers/clients (to simultaneously access the same file), the permissionflag 815 and lock state type 820 is associated (in the session data 802)with a specific combination of a particular client ID 810 (or user ID805) and a particular file handle 812. In some embodiments, eachcombination of a particular client ID 810 (or user ID 805) and aparticular file handle 812 and the associated permission flag 815 andlock state type 820 may comprise a single entry in the disk elementsession data 802. In these embodiments, the entries of the disk elementsession data 802 may be indexed by the combination of a client ID 810(or user ID 805) and a file handle 812.

As discussed above, after the initial access request for file N (whichis used to produce the file handle 812), the client 180 then includesthe client ID 810 and the file handle 812 in subsequent access requestsfor file N. The client ID 810 may be used to interface with the networkelement 310 (e.g., by using the VIF specified by the client ID 810). Thenetwork element 310 receives the access request from the client and usesthe disk element ID in the file handle to identify which disk element350 to route the access request. The network element 310 then sends theaccess request (having the client ID 810 and the file handle 812) to theappropriate disk element 350 to validate and perform the access request.

The disk element 350 may validate the access request by locating anentry (“matching entry”) in the disk element session data 802 indexed bythe received client ID 810 and file handle 812 combination. The diskelement 350 may then analyze the permission flag 815 and lock state type820 (as found in the matching entry) that is associated with the clientID 810 and file handle 812 combination. By doing so, the disk element350 may determine whether the received access request is valid (i.e.,the user/client 180 has permission to perform the specific accessrequest on the requested file N). If so, the disk element 350 performsthe access request.

As discussed above, the lock metadata in the file inode may specify whattype of lock a user or user type can obtain when accessing the file,such as exclusive (E), shared (S), or none (N). Assuming the client 180(specified by the user ID 805) has permission to access the requestedfile N (specified by the file handle 812), the disk element 350 mayrecord the lock state type 820 given to the client 180 for requestedfile N. Lock state data 820 may be stored to session data 800 to providedata consistency across multiple data-access sessions with multipleclients 180. Where two or more clients 180 may simultaneously attempt towrite to the same file, the lock state data 820 may be used to determinewhich client (if any) is permitted to write to the file and to preventtwo simultaneous write requests being performed on the same file (whichwould cause data inconsistency).

For example, a first client 180 may be given an exclusive lock state onfile N, which is reflected in the lock state data 820 for the firstclient 180 (as identified by the user ID 805 or client ID 810) in thesession data 800. As such, a subsequent second client 180 will not begiven an exclusive lock state on file N, which is reflected in the lockstate data 820 for the second client 180 in the session data 800. Ifboth the first and second clients attempt to perform a write request onfile N, the disk element 350 will check the lock state data 820 in thesession data 800 to determine which client (if any) is permitted towrite to file N. In this example, the disk element 350 will determinethat only the first client has the exclusive lock state and is permittedto write to file N, thus preventing two clients from writing to the samefile at the same time.

B. Dropped Connections

During a client data-access service, however, the connection between theclient 180 and the network element 310 may be dropped/disconnectedwhether intentionally or unintentionally. For example, clientconnections may be intentionally dropped when performing servicing ofthe N-Blades or disk element software components of the nodes of thecluster. Under previous network file protocols (such as SMB 1.0) inprevious Windows® operating systems installed on clients 180), upon anetwork disconnection, the client 180 was configured to immediatelydrop/delete the file handle(s) obtained by the client 180. Also, when aconnection failed, SMB 1.0 nodes were configured to close all open filehandles. As such, for each disconnected client, each previous filehandle must be reproduced.

In the current network file protocols (such as SMB 2.0 in currentWindows® operating systems installed on clients 180), upon a networkdisconnection, the client 180 is configured to drop/delete the filehandle(s) obtained by the client 180 only after a predetermined gracetime period after the initial connection failure occurs. During thispredetermined grace period, the client 180 may also be configured toautomatically perform a predetermined number of reconnection attempts(e.g., 5 attempts under SMB 2.0). If a reconnection is not successfulafter the predetermined number of reconnection attempts, the client 180may be configured to drop/delete the previous file handle(s) obtained bythe client 180. If within the predetermined number of reconnectionattempts, a reconnection is successful, the client 180 may be configuredto retain the previous file handles and re-use the file handles toaccess the same files, without needing to re-open the files andreproduce new file handles. The file handles under of SMB 2.0 aresometimes referred to as “durable file handles.” The durable filehandles feature was designed to allow clients 180 to retain file handlesfor a grace period after a network disconnect to increase thereliability of the protocol when used over networks experiencingfrequent network disconnects (such as wireless networks).

When the network element and disk element software components of a nodeare being serviced (referred to herein as the “serviced” networkelement, disk element, and node), the serviced node may be considered tohave “failed” since it may be taken offline for servicing. As such, thepartner node (and thereby the partner network element and partner diskelement) are configured to take over the work load of the serviced node,whereby the partner network element begins performing the functionspreviously performed by the serviced network element and the partnerdisk element begins performing the functions previously performed by theserviced disk element. Note that the partner disk element is allowed toaccess the data aggregate 510 of the serviced disk element in afailover-type event (such as servicing of the disk element).

Conventionally, the disconnected clients may attempt to reconnect withthe partner node to access files serviced by the partner node that werepreviously requested (and which file handles were obtained). Inparticular, a disconnected client may attempt to reconnect with thepartner network element using the previously obtained client ID(referred to as the “original” client ID) and attempt to re-accesspreviously requested files using the file handles (referred to as the“original” file handles) stored to the client 180. The system aggregate500 associated with the partner node, however, will not have the sessiondata 800 that was collected and stored by the serviced node (which isstored on the system aggregate 500 associated with the serviced node),and thus the partner node will not have access to the session data 800of the serviced node.

As such, the partner network element will not have access to the networkelement session data 801 collected by the serviced network element,which includes user IDs 805 and “original” client IDs 810 of clients 180that were previously connected to the serviced network element and arenow attempting reconnection to the partner network element. Since thepartner network element does not have access to this network elementsession data 801 of the serviced network element, the partner networkelement will not recognize the original client IDs 810 sent by theclients 180 attempting reconnection to the partner network element andmay refuse the reconnection of the clients 180. As such,re-authentication of the client connection may need to be performed anda “new” client ID produced. For example, the client 180 may submit auser ID and password and the partner network element may verify that theuser ID has permission to connect to the cluster 100 and then produce anew client ID.

Similarly, the partner disk element will not have access to the diskelement session data 802 collected by the serviced disk element, whichincludes original client IDs 810 and original file handles 812 obtainedby clients 180 that were previously connected to the serviced diskelement, along with permission data 815 and lock state data 820associated with each client ID 810 and file handle 812 combination. Theclients 180 may then attempt to access the previously opened/accessedfiles using access requests containing the original client IDs 810 andoriginal file handles 812, the access requests being sent to the partnerdisk element for processing. However, since the partner disk elementdoes not have access to this disk element session data 801 of theserviced disk element, the partner disk element will not recognize theoriginal client IDs 810 and original file handles 812 in the accessrequests and will not be able to validate and perform the accessrequests. As such, generation of new file handles for the previouslyopened/accessed files may need to be performed. For example, the client180 may submit a virtual address of the requested file and the networkelement 310 and disk element 350 may translate/map the virtual addressto a file handle (physical address) of the requested file.

As described above, since the partner network element will not haveaccess to the network element session data 801 of the serviced networkelement, re-authentication of connections for clients 180 attemptingreconnection to the partner network element may need to be performed(whereby a new client ID produced). Also, since the partner disk elementwill not have access to the disk element session data 802 of theserviced disk element, re-generation of file handles for the previouslyopened/accessed files may need to be performed. So during servicing ofthe network element and disk element software components of a node,although the original client IDs and file handles may have been retainedby the clients 180 through the network disconnection, they may beuseless since the partner network element and partner disk element willnot recognize the original client IDs and file handles and new clientIDs and file handles may need to be produced regardless. Therefore,conventionally, servicing of the network element and disk elementsoftware components of a node may be substantially disruptive to clients180 using the node 200.

V. Servicing of Software Components of a Node

In some embodiments, the storage operating system 300 comprises aservicing module 400 for performing servicing on the network element 310and/or disk element 350 software components of one or more nodes 200 ofa cluster. For example, the servicing module 400 may perform upgrading,re-installing, maintenance, repairing, etc. of the network element 310and/or disk element 350 software components of a node. The networkelement 310 and disk element 350 may each comprise a servicing module400. The servicing modules 400 in each network element/disk element mayoperate in conjunction to perform servicing of the network element 310and/or disk element 350. For example, the servicing modules 400 mayissue CF messages or other commands to the network element 310 and diskelement 350 to perform the methods described herein. After initiation(e.g., by an administrative command received at message interface 450),the servicing modules 400 may do so automatically (without humanintervention) for one or more nodes 200 of a cluster 100 with reduceddisruption to clients 180 connected to the nodes 200.

For illustrative purposes, in the description below, the network elementand/or disk element of node A are being serviced and are referred to asthe “serviced” network element and disk element. Node A isassigned/associated with system aggregate A and data aggregate A. Theserviced N-Blade stores and uses N-Blade session data A 801 in systemaggregate A and the serviced disk element stores and uses disk elementsession data A 802 in system aggregate A. The serviced disk element alsoservices data in data aggregate A in response to received accessrequests.

For illustrative purposes, in the description below, Node B is thepredetermined failover partner of node A. As such, the network elementand disk element of node B are referred to as the “partner” networkelement and disk element. The partner network element is configured tobegin performing the functions of the serviced network element upon theserviced network element being taken offline. Likewise, the partner diskelement is configured to begin performing the functions of the serviceddisk element upon the serviced disk element being taken offline. Node Bis assigned/associated with system aggregate B and data aggregate B. Theserviced N-Blade stores and uses N-Blade session data B 801 in systemaggregate B and the partner disk element stores and uses disk elementsession data 802 in system aggregate B. The partner disk elementservices data in data aggregate B in response to received accessrequests. The partner disk element is also configured to service data indata aggregate A upon the serviced disk element being taken offline.

For illustrative purposes, in the description below, a client 180 isconfigured under current network file protocols (such as SMB 2.0). Inthese embodiments, upon a connection failure with a network element, theclient 180 is configured to retain a client ID and any file handles (foraccessing particular files) received prior to the connection failure fora predetermined grace time period. During this predetermined graceperiod, the client 180 may also be configured to automatically perform apredetermined number of reconnection attempts (e.g., 5 attempts underSMB 2.0). If a reconnection is successful, the client 180 may beconfigured to retain the previous client ID and file handles and re-usethe previous client ID and file handles to access the same files.

In some embodiments, only the network element 310 software component ofone or more nodes 200 of a cluster is serviced. In other embodiments,only the disk element 350 software component of one or more nodes 200 ofa cluster is serviced. In further embodiments, the network element 310and disk element 350 software components of one or more nodes 200 of acluster are serviced. It may be desirable to service only the networkelement 310 or only the disk element 350 in some situations. Forexample, if there is only an upgrade available for the network element310, or only the network element 310 requires repair, it is desirable toonly service the network elements 310 of the cluster 100 without alsotaking the disk elements 350 offline for servicing. This is advantageoussince the network element 310 and disk element 350 of a node can stilloperate while the other is being serviced.

VI. Servicing of N-Blade Software Component of a Node

FIG. 9A-C show conceptual diagrams of processes performed for servicingof the network element 310 software component of one or more nodes 200of a cluster 100. Servicing of the network element 310 may be initiated,for example, by administrative command received at message interface 450specifying servicing of the network element 310. The servicing modules400 in the network element 310 and disk element 350 may then perform (inconjunction) the servicing automatically (without human intervention)for one or more nodes 200 of a cluster 100. Upon initiation, servicingof the network elements of the cluster 100 begins with a first node(serviced node A), and is repeated for each node of the cluster.

As shown in FIG. 9A, the servicing module 400 may take the servicednetwork element 350 of node A offline (as indicated by the “X” markthrough the connections of the serviced network element 350) so it canno longer perform client data-access sessions (i.e., can no longerreceive or send data relating to client data-access sessions). As such,the serviced network element 350 can no longer receive access requestsfrom clients 180 and route the access requests to the appropriate diskelement 310.

Taking the serviced network element 350 offline also closes all networkports 410 of the serviced network element 350. Doing so prevents clients180 from making new network connections to the serviced network element350 and forces network disconnection with all clients 180 currentlyconnected to the serviced network element 350 for a data-access session.As discussed above, the network ports 410 may be implemented as VIFs. AVIF may transparently change association from one network port 410 toanother network port 410 within the same node 200 or across differentnodes 200. As shown in FIG. 9A, any VIFs of the closed network ports 410of the serviced network element 310 may migrate/change association toopen network ports 410 of the partner network element 310. In this way,as shown in FIG. 9B, data-access to any clients 180 formerly connectedto the serviced network element 310 may connect to the partner networkelement 310 for continuing a data-access session. The serviced networkelement 350 software component then begins to be serviced. For example,the serviced network element 350 may be upgraded (by loading new networkelement 350 software on the serviced node A), re-installed,maintenanced, or repaired.

The servicing module 400 may then provide access to session data A tothe partner network element 310. For example, as shown in FIG. 9A, theservicing modules 400 may begin transferring N-Blade session data A 801stored in system aggregate A to system aggregate B for storage. In someembodiments, the N-Blade session data A 801 is transferred through anetwork, such as the cluster switching fabric 150. For example, theservicing module 400 on serviced node A may send a CF message to theservicing module 400 on partner node B to prepare to receive sessiondata. The servicing module 400 on serviced node A may then begin sendingthe N-Blade session data A 801 from system aggregate A to partner node Bthrough the cluster switching fabric 150. The servicing module 400 onpartner node B then receives and stores the N-Blade session data A 801to its system aggregate B. As such, the partner N-Blade 310 will haveaccess to the N-Blade session data A 801 stored in system aggregate B.Thus, the partner N-Blade 310 will have access to the user IDs 805,client IDs 810, and the file handles 812 obtained by clients 180previously connected to the serviced N-Blade 310.

Each client 180 previously connected to the serviced N-Blade 310 willexperience a network disconnection (upon the forced disconnection) andwill begin to attempt reconnections (e.g., 5 attempts under SMB 2.0)with the partner network element 350 (while retaining any client ID 810and file handles 812 received from the serviced network element 350prior to the network disconnection). Each disconnected client 180 mayattempt reconnections with the partner network element 350 using theclient ID 810 received from the serviced network element 350 prior tothe network disconnection.

If the N-Blade session data A 801 has not been transferred to systemaggregate B yet, the partner network element will not have access to thenetwork element session data A 801 yet. Thus, the partner networkelement will not recognize the client IDs 810 sent by the clients 180attempting reconnection to the partner network element and may refusethe reconnection of the clients 180. Typically, however, the networkelement session data A 801 will be transferred to system aggregate Bwithin the predetermined grace time period and the 5 attemptedreconnections under SMB 2.0.

Once the network element session data A 801 is transferred to systemaggregate B, the partner network element will have access to the networkelement session data A 801 and will then recognize the client IDs 810sent by the clients 180 attempting reconnection. As such, the partnernetwork element will begin accepting the connection attempts based onthe received client IDs and session data A. For example, the partnernetwork element may compare a received client ID with the client IDs innetwork element session data A 801. If a matching client ID is found innetwork element session data A 801, the partner network element mayaccept the connection attempt. Thus, the partner network element mayaccept the connection of a client using an original client ID withouthaving to perform the connection authentication procedure with theclient (whereby re-authentication of the client connection andgeneration of a new client ID would need to be performed). However, if amatch is not found, the partner network element may refuse theconnection attempt (based on the client ID) and require that the clientre-perform the connection authentication procedure.

After a client 180 is reconnected with the partner network element 310(as shown in FIG. 9B), the partner network element 310 begins receivingaccess requests from the client 180. The received access requests maycontain the original client ID and original file handles (for previouslyopened files) received from the serviced network element 310 (which theclient retained as part of the durable handles feature of SMB 2.0). Thepartner network element then processes the access requests based on theoriginal file handles (e.g., by routing, using the original filehandles, the access requests to the appropriate disk element 350 forprocessing).

The receiving disk element 350 uses the original client ID and originalfile handle to validate the access request to a previously opened file(e.g., by analyzing the permission and lock state data associated withthe original client ID and original file handle combination). As such,the original file handles may be used to access client's previouslyopened files, without requiring closing of previously opened files andgeneration of new file handles for the previously opened files by thepartner node. Also, the permission and lock type of the requested filedoes not need to be re-determined for the client 180.

While servicing the reconnected clients 180, the partner network element310 may collect and store new information to the N-Blade session data A801. For example, a reconnected client 180 may request access to a newfile, whereby a new file handle 812 is produced and stored to theN-Blade session data A 801. As such, during the servicing of servicednetwork element 310, the partner network element 310 collects N-Bladesession data A 801 and N-Blade session data B 801 which are both storedin system aggregate B. In these embodiments, N-Blade session data A 801and N-Blade session data B 801 are kept separate (e.g., in differentdata structures) in system aggregate B so the data does not intermingle.

Upon the servicing of the serviced network element being completed, theservicing modules 400 then begin to transfer N-Blade session data A 801(which may or may not contain new information) stored in systemaggregate B to system aggregate A for storage (as shown in FIG. 9C). Theservicing modules 400 may use similar data transfer methods describedabove. The serviced network element 350 is then brought back online soit can resume client data-access sessions by receiving access requestsfrom clients 180 and routing the access requests to the appropriate diskelement 310 (as shown in FIG. 9C). The serviced network element 310 maydo so using the N-Blade session data A 801. As shown in FIG. 9C, for theclients 180 previously connected with the serviced network element, theVIFs that currently connect these clients 180 with the partner networkelement are changed back to associate to a network port 410 on theserviced network element.

The above process may be repeated for each node in the cluster, wherebyeach network element in the cluster is serviced in turn. For example, ifthe cluster comprises node A and node B, each being the failover partnerof the other, the above process would be repeated where node A isreplaced by node B and vice versa. By performing servicing on one nodein the cluster at a time, the entire cluster system does not need to betaken offline, thus reducing disruption to client data-access.

FIGS. 10A-B are flowcharts of a method 1000 for performing servicing onthe network element 310 software component of one or more nodes 200 of acluster. In some embodiments, some of the steps of the method 1000 areimplemented by software or hardware. In some embodiments, some of thesteps of method 1000 are performed by the servicing modules 400 of thenetwork element 310 and disk element 350 software components. The orderand number of steps of the method 1000 are for illustrative purposesonly and, in other embodiments, a different order and/or number of stepsare used.

The method 1000 begins when servicing of the network element 310 isinitiated (at step 1005). For example, servicing may be initiated by anadministrative command received by a message interface module 450. Insome embodiments, after initiation, some or all of the servicing stepsmay be performed automatically (without human initiation orintervention) for one or more nodes 200 of a cluster 100. Uponinitiation, servicing of the network elements of the cluster 100 beginswith a current node (serviced node A) having a partner node (partnernode B), and is repeated for each node of the cluster.

The serviced network element 350 of node A is then taken offline (atstep 1010) so it can no longer perform client data-access sessions(i.e., can no longer receive access requests from clients 180 and routethem to the appropriate disk element 310), whereby all network ports 410of the serviced network element 350 are closed. Closing the networkports 410 forces a network disconnection with all clients 180 currentlyconnected to the serviced network element 350 for a data-access session.The VIFs of the closed network ports 410 of the serviced network element310 then migrate/change association (at 1015) to open network ports 410of the partner network element 310 of node B. Each disconnected client180 will begin to attempt reconnections (e.g., 5 attempts under SMB 2.0)with the network ports 410 of the partner network element 350 (whilealso retaining any “original” client ID 810 and file handles 812received from the serviced network element 350 prior to the networkdisconnection).

After the serviced network element 350 is taken offline, the method 1000begins servicing (at 1020) the serviced network element 350 softwarecomponent (e.g., upgrading, etc.). Also, the method 1000 beginstransferring (at 1025) the N-Blade session data A 801 stored in systemaggregate A to system aggregate B for storage (e.g., transferred throughthe cluster switching fabric 150). This is to provide access to N-Bladesession data A 801 to the partner network element. Note that the N-Bladesession data A 801 will contain the original client IDs 810 and filehandles 812 given to the disconnected clients 180 during data-accesssessions with the serviced N-Blade of node A. While the N-Blade sessiondata A 801 is being transferred, the partner network element 350 willreceive and refuse (at step 1030) connection requests from thedisconnected clients 180 using the original client IDs 810 and filehandles 812. Since the partner network element 350 does not yet haveaccess to the N-Blade session data A 801, the partner network element350 will not recognize the client IDs 810 and may refuse the connectionrequests.

At step 1035, the transfer of network element session data A 801 tosystem aggregate B is completed. As such, the partner network element ofnode B will now have access to the network element session data A 801and will then recognize the client IDs 810 sent by the clients 180attempting reconnection. As such, the partner network element will thenbegin accepting (at 1040) the connection attempts of the disconnectedclients 180 based on the received original client IDs and N-Bladesession data A 801. For example, the partner network element may comparereceived client IDs with the client IDs in network element session dataA 801. If a matching client ID is found in network element session dataA 801, the partner network element may accept the connection attempt bythe client 180 sending the matching client ID. Thus, re-performing ofthe connection authentication procedure may be avoided (wherebyre-authentication of the client connection and generation of a newclient ID is performed). However, if a match is not found, the partnernetwork element may refuse the connection attempt (based on the clientID) and require that the client re-perform the connection authenticationprocedure.

The partner network element 310 then begins receiving (at 1045) accessrequests (containing the original client ID and original file handles)from the reconnected clients 180 and routing (using the original filehandles) the access requests to the appropriate disk element 350. Thereceiving disk element 350 uses the original client IDs and originalfile handles in the access requests to validate and perform (at 1050)the access requests to previously opened files stored on its dataaggregate (e.g., by analyzing the permission and lock state dataassociated with original client ID and original file handle combinationsin its session data 802). While servicing the reconnected clients 180,the partner network element 310 may collect and store (at 1055) newinformation to the N-Blade session data A 801 (e.g., new file handles),whereby the N-Blade session data A 801 and N-Blade session data B 801are kept separate in system aggregate B so the data does notintermingle.

Upon the servicing of the serviced network element being completed, theservicing modules 400 then begin to transfer (at 1060) N-Blade sessiondata A 801 (which may or may not contain new information) stored insystem aggregate B to system aggregate A for storage. The servicednetwork element 350 is then brought back online (at 1065) and, for theclients 180 previously connected with the serviced network element, theVIFs that currently connect these clients 180 with the partner networkelement are changed back to associate to a network port 410 on theserviced network element. The serviced N-Blade then resumes (at 1070)client data-access sessions by receiving access requests from clients180 and routing the access requests to the appropriate disk element 310using the transferred N-Blade session data A 801. Then method 1000 thenends. The method 1000 may be repeated for each node in the cluster,whereby each network element in the cluster is serviced in turn. Byperforming servicing on one node in the cluster at a time, the entirecluster system does not need to be taken offline, thus reducingdisruption to client data-access.

VII. Servicing of Disk Element Software Component of a Node

FIG. 11A-C show conceptual diagrams of processes performed for servicingof the disk element 350 software component of one or more nodes 200 of acluster 100. Prior to servicing, the serviced disk element 350 of node Ahas stored session data A 802 (e.g., comprising “original” client IDsfile handles and permission and lock state data) to the system aggregateA and the partner disk element of node B has stored session data B tothe system aggregate B. Also, the serviced disk element services datafrom data aggregate A and the partner disk element services data fromdata aggregate B in the shared storage.

Prior to servicing, session data A may contain one or more file handlesproduced by the serviced node for one or more files (stored on theshared storage) that were accessed using the serviced disk element. Eachfile handle for a file may be produced by the serviced node for a clientsubmitting an initial access request for the file. The file handle maybe produced during an access request validation procedure (performed bythe serviced disk element) that validates the initial access request(e.g., by determining permission and lock type associated with theclient submitting the initial access request).

Servicing of the disk element 350 may be initiated, for example, byadministrative command received at message interface 450 specifyingservicing of the disk element 350. The servicing modules 400 in thenetwork element 310 and disk element 350 may then perform (inconjunction) the servicing automatically (without human intervention)for one or more nodes 200 of a cluster 100. Upon initiation, servicingof the disk elements of the cluster 100 begins with a first node(serviced node A), and is repeated for each node of the cluster.

As shown in FIG. 11A, serviced disk element 350 of node A is takenoffline (as indicated by the “X” mark through the connections of theserviced disk element 350) so it can no longer perform clientdata-access sessions. As such, the serviced disk element 350 can nolonger receive or perform access requests on the data aggregate A. Eachnetwork element 310 in the cluster is also configured to automaticallybegin to route their access requests to the partner disk element 350 inthe event the serviced disk element 350 fails or is taken offline.

For every client 180 having an open file handle (as reflected in theD-Blade session data A 802) for a file stored on data aggregate A and isaccessing the file using a particular network element, the networkconnection with the client 180 and the particular network element 310 isforced to disconnect by closing the network port 410 that the client 180is connected with. As such, each client 180 currently accessing a fileusing the serviced disk element is disconnected. This may be performedby collecting all client IDs 810 from the disk element session data A802 (stored in system aggregate A) and disconnecting all clients 180having the collected client IDs 810 from all network elements 310 of thecluster. This may be performed for each network element 310 bydetermining client IDs 810 in its N-Blade session data 802 (stored inits associated system aggregate) that match the collected client IDs810, and disconnecting each of these clients 180. In the example of FIG.11A, the client 180 connected with the network element of node A has anopen file handle for a file stored on data aggregate A (i.e., has aclient ID 802 listed in disk element session data A 802. Thus thenetwork connection between the client 180 and the network element ofnode A is forcibly disconnected. In some embodiments, the closed networkports 410 are kept closed until transfer of disk element session data A802 to system aggregate B (discussed below) is completed.

The serviced disk element 350 software component then begins to beserviced. For example, the serviced disk element 350 may be upgraded (byloading new disk element 350 software on the serviced node A),re-installed, maintenanced, or repaired. As shown in FIG. 11A, theservicing modules 400 then begin transferring disk element session dataA 802 stored in system aggregate A to system aggregate B for storage. Insome embodiments, the disk element session data A 802 is transferredthrough a network, such as the cluster switching fabric 150 (asdescribed above).

Each disconnected client 180 will begin to attempt reconnections (e.g.,5 attempts under SMB 2.0) with the network element 310 it was previouslyconnected with (while retaining any client ID 810 and file handles 812received prior to the network disconnection). Each disconnected client180 may attempt reconnections using the retained client ID 810. In someembodiments, the closed network ports 410 (causing the networkdisconnections) of the network elements 310 are kept closed untiltransfer of disk element session data A 802 to system aggregate B iscompleted. Until the network ports are re-opened, the attemptedreconnections of each client 180 will fail. Typically, however, the diskelement session data A 802 will be transferred to system aggregate Bwithin the predetermined grace time period and the 5 attemptedreconnections under SMB 2.0.

Once the disk element session data A 802 is completely transferred tosystem aggregate B, the network ports are re-opened and the disconnectedclients will reconnect with their respective network elements 310 (asshown in FIG. 11B). The partner disk element 350 will now have access tothe disk element session data A 802 stored in system aggregate B. Thus,the partner disk element 350 will have access to the client IDs 810,file handles 812, permission flag 815 and lock state type 820 datacollected for clients 180 for files stored on data aggregate A. Thepartner disk element will also be configured to have access to dataaggregate A upon failure of the serviced disk element (as well as accessto data aggregate B per usual).

As shown in FIG. 11B, after the disk element session data A 802 iscompletely transferred to system aggregate B, the partner disk element350 may begin servicing data on data aggregate A using the disk elementsession data A 802. In particular, the partner disk element 350 maybegin receiving access requests from the disconnected clients 180. Thereceived access requests may contain the original client ID and originalfile handles for previously opened files on data aggregate A. Thepartner disk element 350 may use the original client ID 810 and originalfile handle 812 to validate an access request to a previously openedfile (e.g., by analyzing the permission data 815 and lock state data 820associated with the original client ID and original file handlecombination in the disk element session data A 802). Thus the partnerdisk element accesses the previously opened files using the originalclient ID and original file handles, without having to perform an accessrequest validation procedure for the previously opened files and withouthaving to produce new file handles for the previously opened files.Also, the permission and lock type of the requested file does not needto be re-determined for the client 180.

While servicing data on data aggregate A, the partner disk element 350may collect and store new information to the disk element session data A802. For example, a reconnected client 180 may request access to a newfile, whereby a new file handle 812, new permission data 815, and newlock state data 820 is produced and stored to the disk element sessiondata A 802. As such, during the servicing of serviced disk element 350,the partner disk element 350 collects disk element session data A 802and disk element session data B 802 which are both stored in systemaggregate B. In these embodiments, disk element session data A 802 anddisk element session data B 802 are kept separate (e.g., in differentdata structures) in system aggregate B so the data does not intermingle.

Upon the servicing of the serviced disk element being completed, theservicing modules 400 then begin to transfer disk element session data A802 (which may or may not contain new information) stored in systemaggregate B to system aggregate A for storage (as shown in FIG. 11C).The servicing modules 400 may use similar data transfer methodsdescribed above. The serviced disk element 350 is then brought backonline so it can resume servicing data on data aggregate A by receivingaccess requests (from network elements 310) and performing accessrequests on files stored in data aggregate A (as shown in FIG. 9C). Theserviced disk element 350 may do so using the disk element session dataA 802. Each network element 310 in the cluster is also configured toautomatically begin to route their access requests to the serviced diskelement 350 once the serviced disk element 350 is brought back online.

The above process may be repeated for each node in the cluster, wherebyeach disk element in the cluster is serviced in turn. For example, ifthe cluster comprises node A and node B, each being the failover partnerof the other, the above process would be repeated where node A isreplaced by node B and vice versa. If both the network element 310 anddisk element 350 software components of the nodes 200 of a cluster areto be serviced, the above described method for servicing the networkelement and the method for servicing the disk element can be performedon each node. This process may be repeated for each node in the cluster,whereby each node in the cluster is serviced one after the other. Byperforming servicing on one node in the cluster at a time, the entirecluster system does not need to be taken offline, thus reducingdisruption to client data-access.

FIGS. 12A-B are flowcharts of a method 1200 for performing servicing onthe disk element 350 software component of one or more nodes 200 of acluster. In some embodiments, some of the steps of the method 1200 areimplemented by software or hardware. In some embodiments, some of thesteps of method 1200 are performed by the servicing modules 400 of thenetwork element 310 and disk element 350 software components. The orderand number of steps of the method 1200 are for illustrative purposesonly and, in other embodiments, a different order and/or number of stepsare used.

The method 1200 begins when servicing of the disk element 350 isinitiated (at step 1205). For example, servicing may be initiated by anadministrative command received by a message interface module 450. Insome embodiments, after initiation, some or all of the servicing stepsmay be performed automatically (without human initiation orintervention) for one or more nodes 200 of a cluster 100. Uponinitiation, servicing of the disk elements of the cluster 100 beginswith a current node (serviced node A) having a partner node (partnernode B), and is repeated for each node of the cluster.

The serviced disk element 350 of node A is then taken offline (at step1210) so it can no longer perform client data-access sessions and can nolonger receive or perform access requests on the data aggregate A. Eachnetwork element 310 in the cluster is also configured to automaticallybegin to route their access requests to the partner disk element 350 inthe event the serviced disk element 350 fails or is taken offline. Forevery client 180 having an open file handle (as reflected in the diskelement session data A 802) for a file stored on data aggregate A and isaccessing the file using a particular network element, the networkconnection with the client 180 and the particular network element 310 isdisconnected (at step 1215) by closing the respective network ports 410,whereby the closed network ports 410 are kept closed until transfer ofdisk element session data A 802 to system aggregate B is completed. Assuch, each client currently accessing a file using the serviced diskelement is disconnected (at step 1215). Each disconnected client 180 isconfigured to begin to attempt reconnections with the respective networkelement 310 (while also retaining any original client ID 810 and filehandles 812).

The method 1200 begins servicing (at 1220) the serviced disk element 350software component (e.g., upgrading, etc.). Also, the method 1200 beginstransferring (at 1225) the disk element session data A 802 stored insystem aggregate A to system aggregate B for storage. This is to provideaccess to disk element session data A 802 to the partner disk element.Upon the disk element session data A 802 being completely transferred tosystem aggregate B, the network ports are re-opened (at step 1230). Thepartner disk element 350 will now have access to the disk elementsession data A 802 (stored in system aggregate B) for files stored ondata aggregate A. The partner disk element will also be configured tohave access to data aggregate A upon failure of the serviced diskelement.

The disconnected clients will reconnect (at step 1235) with theirrespective network elements 310. The partner disk element 350 may beginservicing data (at step 1240) on data aggregate A using the disk elementsession data A 802 by receiving access requests (containing originalclient ID and original file handles for previously opened files on dataaggregate A) from the reconnected clients 180. The partner disk element350 may use the original client ID 810 and original file handle 812 tovalidate an access request to a previously opened file (e.g., byanalyzing the permission data 815 and lock state data 820 associatedwith the original client ID and original file handle combination in thedisk element session data A 802).

While servicing the reconnected clients 180, the partner disk element350 may collect and store (at 1245) new information to the disk elementsession data A 802, whereby the disk element session data A 802 and diskelement session data B 802 are kept separate in system aggregate B sothe data does not intermingle. Upon the servicing of the serviced diskelement being completed, the servicing modules 400 then begin totransfer (at 1250) disk element session data A 802 stored in systemaggregate B to system aggregate A for storage. The serviced disk element350 is then brought back online (at 1255) and resumes servicing data ondata aggregate A using the disk element session data A 802.

Then method 1200 then ends. The method 1200 may be repeated for eachnode in the cluster, whereby each disk element in the cluster isserviced in turn. If both the network element 310 and disk element 350software components of the nodes 200 of a cluster are to be serviced,the above described method 1000 for servicing the network element andthe method 1200 for servicing the disk element can be performed on eachnode. This process may be repeated for each node in the cluster, wherebyeach node in the cluster is serviced one after the other. By performingservicing on one node in the cluster at a time, the entire clustersystem does not need to be taken offline, thus reducing disruption toclient data-access.

Some embodiments may be conveniently implemented using a conventionalgeneral purpose or a specialized digital computer or microprocessorprogrammed according to the teachings of the present disclosure, as willbe apparent to those skilled in the computer art. Appropriate softwarecoding may readily be prepared by skilled programmers based on theteachings of the present disclosure, as will be apparent to thoseskilled in the software art. Some embodiments may also be implemented bythe preparation of application-specific integrated circuits or byinterconnecting an appropriate network of conventional componentcircuits, as will be readily apparent to those skilled in the art.

Some embodiments include a computer program product which is a storagemedium (media) having instructions stored thereon/in which may be usedto control, or cause, a computer to perform any of the processes of anembodiment. The storage medium may include without limitation any typeof disk including floppy disks, mini disks (MD's), optical disks, DVDs,CD-ROMs, micro-drives, and magneto-optical disks, ROMs, RAMs, EPROMs,EEPROMs, DRAMs, VRAMs, flash memory devices (including flash cards),magnetic or optical cards, nanosystems (including molecular memory ICs),RAID devices, remote data storage/archive/warehousing, or any type ofmedia or device suitable for storing instructions and/or data.

Stored on any one of the computer readable medium (media), someembodiments include software for controlling both the hardware of thegeneral purpose/specialized computer or microprocessor, and for enablingthe computer or microprocessor to interact with a human user or othermechanism utilizing the results of an embodiment. Such software mayinclude without limitation device drivers, operating systems, and userapplications. Ultimately, such computer readable media further includessoftware for performing some embodiments, as described above. Includedin the programming (software) of the general/specialized computer ormicroprocessor are software modules for implementing the teachings ofsome embodiments.

While the embodiments described herein have been described withreference to numerous specific details, one of ordinary skill in the artwill recognize that the embodiments can be embodied in other specificforms without departing from the spirit of the embodiments. Thus, one ofordinary skill in the art would understand that the embodimentsdescribed herein are not to be limited by the foregoing illustrativedetails, but rather are to be defined by the appended claims.

What is claimed is:
 1. A method comprising: receiving, by a clientdevice, a client identifier from a first node within a network of nodesbased upon credentials of the client device being authenticated;transmitting an access request, comprising the client identifier, for afile to the first node; receiving session data, comprising a handle forthe file and the client identifier, from the first node; utilizing thehandle and the client identifier to access the file through the firstnode based upon the session data; and utilizing the handle and theclient identifier to access the file through a second node of thenetwork of nodes based upon the session data being migrated as migratedsession data accessible to the second.
 2. The method of claim 1,comprising: retaining the handle and client identifier based upon adetermination that the session data was migrated.
 3. The method of claim1, wherein the session data is migrated without notifying the clientdevice.
 4. The method of claim 1, wherein the session data comprisespermission data associated with the handle.
 5. The method of claim 1,wherein the session data comprises lock state data associated with thehandle.
 6. The method of claim 1, wherein an application hosted by theclient device is configured to utilize the handle and the clientidentifier to access the file.
 7. The method of claim 1, wherein a filesystem by the client device is configured to utilize the handle and theclient identifier to access the file.
 8. The method of claim 1,comprising: migrating, by the client device, the session data to createthe migrated session data.
 9. The method of claim 8, wherein the clientdevice and the first node are hosted within a first client computingdevice and the second node is hosted within a second client computingdevice.
 10. The method of claim 1, wherein the first node is takenoffline based upon the session data being migrated.
 11. The method ofclaim 10, wherein the first node is taken offline by forcing a networkdisconnect with the client device in order to service the first node.12. A non-transitory machine readable medium comprising instructions forperforming a method, which when executed by a machine, causes themachine to: receive, by a client device, a client identifier from afirst node within a network of nodes based upon credentials of theclient device being authenticated; transmit an access request,comprising the client identifier, for a file to the first node; receivesession data, comprising a handle for the file and the clientidentifier, from the first node; utilize the handle and the clientidentifier to access the file through the first node based upon thesession data; and utilize the handle and the client identifier to accessthe file through a second node of the network of nodes based upon thesession data being migrated as migrated session data accessible to thesecond node.
 13. The non-transitory machine readable medium of claim 12,wherein the instructions cause the machine to: retain the handle andclient identifier based upon a determination that the session data wasmigrated.
 14. The non-transitory machine readable medium of claim 12,wherein the session data is migrated without notifying the clientdevice.
 15. The non-transitory machine readable medium of claim 12,wherein the session data comprises permission data associated with thehandle.
 16. The non-transitory machine readable medium of claim 12,wherein the session data comprises lock state data associated with thehandle.
 17. The non-transitory machine readable medium of claim 12,wherein an application hosted by the client device is configured toutilize the handle and the client identifier to access the file.
 18. Thenon-transitory machine readable medium of claim 12, wherein a filesystem by the client device is configured to utilize the handle and theclient identifier to access the file.
 19. The non-transitory machinereadable medium of claim 12, wherein the instructions cause the machineto: migrate, by the client device, the session data to create themigrated session data.
 20. A computing device comprising: a memorycomprising machine executable code for performing a method; and aprocessor coupled to the memory, the processor configured to execute themachine executable code to cause the processor to: receive a clientidentifier from a first node within a network of nodes based uponcredentials of the computing device being authenticated; transmit anaccess request, comprising the client identifier, for a file to thefirst node; receive session data, comprising a handle for the file andthe client identifier, from the first node; utilize the handle and theclient identifier to access the file through the first node based uponthe session data; and utilize the handle and the client identifier toaccess the file through a second node of the network of nodes based uponthe session data being migrated as migrated session data accessible tothe second node.